Radio frequency identification (“RFID”) systems are used in a plethora of commercial contexts requiring a unique identification system for large numbers of items. Such contexts include everything from department store inventory and check-out systems to the tracking of military supplies to and from the front lines. Similar in utility to bar code technology, RFID systems are often preferred due to their increased range, lack of a line of sight requirement between a tag and its reader and the high multi-tag throughput of RFID readers (i.e., RFID readers may read many tags in their large field of view at very high transport speeds).
A problem that arises is that optimal performance of RFID systems is often hampered by the reflection and coupling which inevitably occur in RF transceivers, in which a significant portion of the transmitted interrogation signal is reflected by the antenna and objects in the environment into the receiving portion of the transceiver. These problems are quantified in a measure called the voltage standing wave ratio (“VSWR”), measured as the non-transmitted (i.e. coupled or reflected from the antenna or non-RFID objects in the environment) power over the total transmitted power of the transceiver. A high VSWR interferes with efficient transceiver performance and may even result in a “blinding” or complete saturation of the receiver. Transceivers designed to minimize VSWR are often unacceptable because of their high cost in terms of size and power, especially in the context of mobile devices.